The use of surgical robots can offer many advantages over traditional surgery. A common use of such systems is in a master-slave configuration. In such systems, a master control is operated by an operator and used to guide the position and orientation of an end effector located at the end of a robotic arm. In such systems a human operator guides a master control, and the input to this master control is used to guide the slave arm of the robot, and often this guidance is used to direct the motion of an end effector at the distal end of the slave arm.
One potential improvement that such systems may offer over traditional surgery is improved precision at the slave site, and considerable efforts have been made towards this end. One set of challenges of such systems are the limitations of the human operator. Several previous devices methods have been devised to work around, or compensate for, some common and innate human limitations.
Several approaches have been used to improve the precision with which a tool can be guided by an operator. One of these methods is filtering applied to the signal from the master controller aimed at reducing the effects of unwanted movement due to hand tremors on the master control, so that the slave tool moves in a way that is less influenced by the tremors. As tremors may cause unintended motion of the tool, the filtered response of the slave may be more consistent with what was intended by the operator, and in this way filtering applied to the signal from the master controller may act to increase the precision with which the slave tool can be controlled.
However, a disadvantage of filtering is that since multiple sequential sensor readings from the master controller may be required as inputs to the filters, and these readings must be taken over a timescale comparable to the tremor cycle, acquiring these additional inputs can incorporate delays into the system. This can delay the motion of the slave tool and visual feedback times, and make interactive control of the tool more difficult. That is, in master-slave systems, the tool is usually guided in a closed loop configuration, where the operator performs a movement of the master controller and then views the resulting motion of the tool (either directly, through a physical device such as a microscope, or through a camera), and delays in this feedback loop hinder closed loop control.
Another method used to increase precision is scaling, wherein the motions of the master control are transmitted to the slave control at a reduced scale. For example, a motion of the master control of 1 cm might direct the slave tool to move 1 mm. Scaling can result in improved precision control at the site of the slave end effector if an operator can guide the master control so that a system where without scaling would give a precision of 1 mm at the slave site, then a system that has a scale factor of 0.1, the precision at the slave site would be approximately 0.1 mm.
A disadvantage of scaling is that it reduces the spatial extent of the region at the site of the slave end effector that can be easily accessed; specifically, the region that can be accessed using a continuous and linearly scaled motion of the master control will have a range of motion reduced by the same scale factor. For example, if the master control has a 10 cm range of motion and the scale factor remains at 0.1, the range of motion at the site of the end effector will be approximately 1 cm. To get around this problem, it may be possible, for example, to “ratchet” the input, by repeatedly engaging and disengaging the link between the master and slave control (similar to lifting a computer mouse to relocate the physical mouse position relative to the cursor). However, this can become tedious if the surgeon has to ratchet many times. Therefore, it remains advantageous to find other approaches to increasing precision.
Accordingly, there is a continuing need in the art for devices and methods that can provide stable, high-precision controlled motion of a tool. The embodiments disclosed herein addresses these needs and others.